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Tue, 7 Jul 2020 15:21:49 +0000 (UTC) Date: Tue, 7 Jul 2020 17:21:47 +0200 From: Kevin Wolf To: Eric Blake Subject: Re: [PATCH] qemu-img map: Don't limit block status request size Message-ID: <20200707152147.GC7002@linux.fritz.box> References: <20200707144629.51235-1-kwolf@redhat.com> <9f74d8dc-9c4e-d519-9dd7-0895ece3de17@redhat.com> MIME-Version: 1.0 In-Reply-To: <9f74d8dc-9c4e-d519-9dd7-0895ece3de17@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 00:46:09 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 07.07.2020 um 16:54 hat Eric Blake geschrieben: > On 7/7/20 9:46 AM, Kevin Wolf wrote: > > Limiting each loop iteration of qemu-img map to 1 GB was arbitrary from > > the beginning, though it only cut the maximum in half then because the > > interface a signed 32 bit byte count. These days, bdrv_block_status() > > supports a 64 bit byte count, so the arbitrary limit is even worse. > > > > On file-posix, bdrv_block_status() eventually maps to SEEK_HOLE and > > SEEK_DATA, which don't support a limit, but always do all of the work > > necessary to find the start of the next hole/data. Much of this work may > > be repeated if we don't use this information fully, but query with an > > only slightly larger offset in the next loop iteration. Therefore, if > > bdrv_block_status() is called in a loop, it should always pass the > > full number of bytes that the whole loop is interested in. > > > > This removes the arbitrary limit and speeds up 'qemu-img map' > > significantly on heavily fragmented images. > > > > Signed-off-by: Kevin Wolf > > --- > > qemu-img.c | 5 +---- > > 1 file changed, 1 insertion(+), 4 deletions(-) > > Do you want this in 5.1? It seems like a nice optimization. I guess now that I have your R-b, I can sneak both patches in for soft freeze. :-) Kevin